A screenshot shows the Apple iTunes page for recently released English-language version of Tecent’s WeChat mobile messaging app.

Speaking during Sina’s earnings call on Friday, chairman Charles Chao said that the time users spent on the company’s Weibo microblogging platform declined slightly in the third quarter from the second quarter, in part due to competition from WeChat. Though analysts have pointed to rising competition between Weibo and WeChat, Mr. Chao’s comment marks the first official indication from either of the companies that the game is on.

Launched in early 2011, WeChat already has more than 200 million users and has helped Tencent claim a healthy chunk of China’s middle- and upper-class users, who do not necessarily use the company’s microblog or QQ desktop-computer messenger services.

That means it is square on Sina’s turf, since Sina Weibo is predominantly used by China’s urban upper crust. Tencent reports larger user numbers for its own microblogging service than Sina does, but most analysts argue that users of Tencent’s Weibo tend to be less wealthy or from smaller cities in China.